Various processes and catalysts exist for the homopolymerization or copolymerization of olefins. For many applications, it is desirable for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. A high weight average molecular weight, when accompanied by a narrow molecular weight distribution, provides a polyolefin with high strength properties.
Traditional Ziegler-Natta catalysts systems—a transition metal compound co-catalyzed by an aluminum alkyl—are typically capable of producing polyolefins having a high molecular weight, but with a broad molecular weight distribution.
More recently a catalyst system has been developed wherein the transition metal compound has one or more cyclopentadienyl ring ligands (typically two)—such transition metal compound being referred to herein as a “metallocene—which catalyzes the production of olefin monomers to polyolefins. Accordingly, titanocenes, zirconocenes and hafnocenes, have been utilized as the transition metal component in such “metallocene” containing catalyst system for the production of polyolefins and ethylene-alpha-olefin copolymers.
Catalysts that produce isotactic polyolefins are disclosed in U.S. Pat. No. 4,794,096. This patent discloses a chiral, stereorigid metallocene catalyst which is activated by an alumoxane cocatalyst which is reported to polymerize olefins to isotactic polyolefin forms. Alumoxane co-catalyzed metallocene structures which have been reported to polymerize alpha-olefins stereoregularly include the ethylene bridged bis-indenyl and bis-tetrahydroindenyl titanium and zirconium (IV) catalyst. Such catalyst systems were synthesized and studied in Wild et al., J. Organomet. Chem. 232, 233-47 (1982), and were later reported in Ewen and Kaminsky et al., mentioned above, to polymerize alpha-olefins stereoregularly. Further reported in West German Off DE 3443087A1 (1986), but without giving experimental verification, is that the bridge length of such stereorigid metallocenes can vary from a C1 to C4 hydrocarbon and the metallocene rings can be simple or bi-cyclic but must be asymmetric. When substituted or unsubstituted indenyl or tetrahydroindenyl based, these metallocenes are bridged in the “1-position” of the (hydro)indenyl ring, and are of C2 symmetry. Generally speaking, it is the C2 symmetric structure (also referred to as the d/l-enantiomers or racemic complexes) that produces isotactic poly-alpha-olefins. An alternate form is the Cs symmetric or meso form that produces atactic poly-alpha-olefins.

The use of metallocene compositions in olefin polymerization is generally known. Metallocenes containing substituted, bridged indenyl derivatives are noted for their ability to produce isotactic propylene polymers having high isotacticity and narrow molecular weight distribution. Considerable effort has been made toward obtaining metallocene produced propylene polymers having ever-higher molecular weight and melting point, while maintaining suitable catalyst activity. Researchers currently believe that there is a direct relationship between the way in which a metallocene is substituted, and the molecular structure of the resulting polymer. For the substituted, bridged indenyl type metallocenes, it is believed that the type and arrangement of substituents on the indenyl groups, as well as the type of bridge connecting the indenyl groups, determines such polymer attributes as molecular weight and melting point. Unfortunately, it is impossible at this time to accurately correlate specific substitution patterns with specific polymer attributes, though minor trends may be identified, from time to time.
For example, U.S. Pat. No. 5,840,644 describes certain metallocenes containing aryl-substituted indenyl derivatives as ligands, which are said to provide propylene polymers having high isotacticity, narrow molecular weight distribution and very high molecular weight.
Likewise, U.S. Pat. No. 5,936,053 describes certain metallocene compounds said to be useful for producing high molecular weight propylene polymers. These metallocenes have a specific hydrocarbon substituent at the 2 position and an unsubstituted aryl substituent at the 4 position, on each indenyl group of the metallocene compound.
Also known in the art are unbridged indenyl based metallocenes having bulky substituents on the indenyl ligand, thus providing “fluxionality” to the activated catalyst. Metallocenes of this type are believed to produce “elastomeric” polypropylene. Science, 1995, 267, 217; WO 95/25757; and Organometallics, 1997, 16, 3635 discuss such catalysts.
References containing aromatic heterocyclic substituents on cyclopentadienyl or indenyl based metallocenes (non-bridged), but that are not bonded to the cyclopentadienyl or indenyl ring via the heteroatom include: Organometallics 2000, 19, 4095; Organometallics 2001, 20, 5067; J. Organometallic Chem. 2001, 622, 143; J. Phys. Org. Chem. 2002, 15, 582; U.S. Pat. No. 6,458,982 B1; EP 1,033,371 A1; US 2001/0031834 A1; U.S. Pat. No. 6,479,646 B1; and US 2002/0002261 A1.
References containing aromatic heterocyclic substituents on cyclopentadienyl or indenyl based metallocenes (bridged), but that are not bonded to the cyclopentadienyl or indenyl ring via the heteroatom include: Chem. Lett. 1999, 1311; U.S. Pat. Nos. 6,169,051 B1; 6,326,493 B1; and WO 00/43406.
References containing non-aromatic heterocyclic substituents on cyclopentadienyl or indenyl based metallocenes (bridged), and that are bonded to the cyclopentadienyl or indenyl ring via the heteroatom include: J. Organometallic Chem. 1996, 519, 269; Organometallics 2000, 19, 1262; U.S. Pat. Nos. 5,756,608; 5,585.509; and EP 0 670 325 B1.
JP3323347B2 discloses specific aromatic heterocyclic substituents (pyrrol-1-yl substituent including ring-fused hydrocarbyl substituted pyrrol-1-yl substituents) on bridged indenyl based metallocenes. U.S. Pat. No. 6,479,646 B1 discloses metallocene compounds having a heteroatom containing substituent off of the indenyl ring. Examples are all to the 2-positions of the cyclic heteroatom group. US 2002/0002261 A1 discloses bis[2-(2-furyl)indenyl]zirconium dichloride and or bis[2-(2-furyl)-4-phenylindenyl]zirconium dichloride for use in making polypropylene. Likewise US 2001/0031834 A1 discloses polypropylene compositions made using indenyl metallocenes. U.S. 2001/0053833 A1 discloses compounds that are bridged indenes that have heterocyclic substituents on the indene. with the proviso that at least one of the heterocyclic substituents has another substituent on it. Examples are all with 2-substitutend heterocycles including bis(2-(2-(5-methyl)-furyl)-4,5-benzoindenyl)zirconium dichloride, bis(2-(2-(5-phenyl)-furyl)-indenyl)zirconium dichloride, rac-dimethylsilylene bis(2-(2-(5-methyl)-furyl)-4-phenylindenyl)zirconium dichloride, and rac-dimethylsilylene bis(2-(2-(5-methyl)-furyl)-indenyl)zirconium dichloride.